pumpkins blooming but not fruiting

i planted two types - jack o lantern and super sweet pie. the vines are growing like crazy and im getting tons of flowers - i guess there are two, the male with pollen and the female that will fruit.
well, as the title suggests, im getting tons of flowers, but the female ends just wither away after blooming. ive even gone to trying to pollenate them myself but nothing.
whats going on here?